A salt glaze is formed by
Answer: C
Sodium chloride volatilises and reacts with the silica of the body surface to form a thin glaze in place. The characteristic orange-peel texture comes from the reaction happening on the surface rather than from an applied layer.
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State whether the following is true or false.
Salt glazing produces a glaze layer that was applied to the ware beforehand.
Answer: D
The glaze forms in place by reaction between vapour and the body surface, so nothing is applied at all. This is what gives the process its characteristic texture and its economy in a single firing. No separate glost firing is needed at all.
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Consider the following statements about glaze faults.
1. Crazing indicates the glaze is in tension.
2. Crawling is usually a wetting problem at application.
3. Pinholing is caused by an expansion mismatch.
Answer: A
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: crazing means the glaze is in tension, and crawling is a wetting failure, where the glaze pulls back from a greasy, dusty or overfired surface leaving bare patches. Statement 3 misattributes pinholing - it is caused by gas escaping through the glaze as it melts, from the body or from decomposing glaze materials, and the remedy lies in the firing schedule rather than in the expansion match.
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Lead release from a glazed article is regulated because
Answer: B
Correct answer: lead can dissolve into food and drink
An acidic food or drink will leach lead from a glaze whose composition or firing leaves it available, and the lead is then ingested. Release limits are therefore set for tableware and tested by extraction with acetic acid. Proper fritting, sufficient silica and alumina in the recipe, and correct firing all reduce the release; underfiring is the common cause of failing the test.
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Assertion (A): An underfired lead glaze is more hazardous than a properly fired one.
Reason (R): Incomplete melting leaves lead in a form more readily attacked by acids.
Answer: C
Both are true and the reason gives the mechanism: firing to the correct temperature locks the lead into the glass network, so the fault is one of process control rather than of the recipe itself. The same glaze fired correctly meets the limits comfortably.
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State whether the following is true or false.
Glaze faults are always caused by the glaze recipe rather than by the process.
Answer: D
Application thickness, surface cleanliness, firing rate and soak all cause faults in a perfectly sound recipe. Diagnosing whether a fault is chemical or procedural is the first step in correcting it. Changing the recipe when the fault is procedural wastes a great deal of time.
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